A Study on the Cold In jury of Azadirach ta indica in theReg iona l Testing Area s of Yunnan Prov ince

Low temperature and cold injury need to be taken into account for the introduction of Azadirachta ind icafrom its native with trop ical climate condition to subtrop ical climate areas. The extremely low temperature is the mostimportant factor to cold damage of A. ind ica. There was no cold injury in areas where the temperature was above 2℃. In the range of 0 ～2 ℃ some sap lings exhibited symp toms of leaf fall and withering. The symp toms of tip,branch withering and stem death occurred as the lowest temperature was below 0 ℃. Cold injurywas exacerbated byheavy frost and ice. An increase in relative humidity aggravated the extent of cold injury. The result from yearly observation of cold damage and the analysis ofmeteorological data shows: branches or stems of trees died to differentdegrees throughout the winter, weak trees died, a few trees blossomed and fruited, and the fruits could not ripenwhen the mean daily minimum temperature lower than or equal to 0 ℃ was more than 1. 5 days within one year.There was no cold injury to trees over 4 years old. Leaves of a few young trees died in the winter if the lowest temper2ature ( below 0 ℃) occurred occasionallywhen the mean dailyminimum temperature ≤0 ℃ drop down to 0 days inone year. When the lowest temperature ranged between 0～2 ℃, young trees blossomed and fruited normally, somedieback occurred, and the tip ormargin of leaflets dried. No symp tom of cold injury occurred when the lowest temperature was above 2 ℃ in the winter. The oldest and strongest treeswere more resistant to the coldness. Trees distributed in the valley-bottoms and on the northern slopes are ap t to be affected by low temperatures.